In a retrospective survey in the Lower Bavarian district (Germany) the prevalence rates for motor, speech, cognitive and psychosocial impairments in six consecutive cohorts of school beginners were estimated. The relationship between these impairments and the duration of preschool attendance and the location of the preschool attended were assessed. Attending preschool for less than one year was a significant risk factor for several types of impairments while children attending an urban preschool had an increased risk of impairment relative to their rural counterparts. Since our data comes from a circumscribed geographical area, it may not be equally applicable to other national or international localities.
Prevalence rates of impairments
In our study about 2.8% girls and 7.3% boys demonstrated one or more motor impairments. Higher rates of impairment of motor development were seen in a previous study of school children in the district Weser-Ems . In this study 6.6% of girls and 12.5% of boys demonstrated deficits of gross motor coordination and 6.2% girls and 17.6% boys had deficits of fine motor coordination. High rates of motor impairments were also found in children in Western German District of Northrhine-Westfalia . In this study about 5.2% (2.191) girls and 11.1% (5.009) boys were assessed as having of problems of motor coordination. Impairment of fine motor coordination was found in 5.6% girls and 4.8% boys in a study of the District of Lower Saxonia (Germany) . Our study, therefore, demonstrated somewhat lower rates of motor abnormalities compared to these other reports. These differences are likely to represent slight differences in school entry examinations and diagnostic procedures rather than differing prevalence rates between these populations, although the possibility of true regional differences cannot be excluded.
In the area of speech development we found that 11.5% children (6.9% girls; 15.1% boys) demonstrated impairment in pronunciation, 2.9% (1.6% girls, 3.9% boys) had impairments in grammar and 3.3% (1.9% girls; 4.4% boys) demonstrated impairments in rhythm of speech. Other reports on children's health have estimated higher rates of speech impairments than our study. A report from the district of Weser Ems for school entry children detected speech impairments in 36.2% girls and 63.8% boys .
To our knowledge, cognition has not been assessed in similar reviews of school entry children. The assessments utilised in our survey involved the systematic categorisation of cognitive deficits into five subgroups. We found no similar or comparable assessments documented in any previous pre-school cohorts. The large numbers of children assessed in our study and the fact that the assessments where carried out by the same medical team blind to the analysis over the study period of six years, adds to the reliability and validity to our findings. Our study indicates significant levels of cognitive impairments in the children assessed. Unfortunately, no data on cognition is available for the comparison of prevalence rates to those of other methodologies. Further studies in this field are required to obtain results for comparisons.
In our study psychosocial deficits were observed in 5.9% children (4.5% girls; 6.8% boys). Lower rates of psychosocial deficits were found in a cohort of school entry children in Northrhine-Westfalia, in 1999 (2.9% girls; 4.6% boys) and in the following year (3.0% for girls; 4.9% for boys) . In contrast to these results, a study in Lower Saxonia detected significant behavioural deficits in 35.5% girls and 64.5% boys . It is likely that the criteria utilised to diagnose psychosocial deficits, are not sufficiently homogenous and validated to allow the comparison of prevalence rates between different studies.
Associations between duration and location of preschool and children's health
In our study, 91.7% of the children beginning school between 1997 and 2002 had visited a preschool before entering the first class of school. Of these children, 98.3% had attended preschool more than one year and while only a small minority of children (1.7%) had attended for less than twelve months. A general trend over time, in our study, was that the proportion of children attending preschool for less than one year declined between 1997 (2.3%) and 1999 (0.9%). In a survey of Lower Saxonia, children entering school had attended preschool for between 2 to 3 years in urban areas and between 1–2 years in rural areas . According to a health report from the city of Mannheim only 2.3% of children had not visited a preschool before entering school . All other children (97.7%) in Mannheim had visited preschool on average for an average of 37 months . In marked contrast to these figures, a survey of children in urban Cologne found only 63% of 10,086 children entering school had visited a preschool .
While previous public health reports on children's health have assessed the duration of preschool attendance for children entering school, they have not attempted to assess the relationship between attendance and the prevalence of developmental impairments [22, 24, 25]. We identified two other small studies which investigated the relationship between duration and location of attending a preschool and the health of pre-school children [20, 28]. Similar to our study, a survey in Brandenburg, Germany,  reported a four-fold risk for impairments in fine and grapho-motor coordination for children who had visited preschool for less than one year. A study by Bruns-Philipps concluded that children who had never visited preschool suffered higher rates of deficits in fine motor coordination than children who had visited for longer than three years . Our study also demonstrated higher rates of cognitive problems in children who had attended preschool for less than a year, however, there were no significant difference between the groups in psychosocial development. Somewhat surprisingly, for impairments of speech it was the children who had attended preschool for less than a year who had slightly lower rates of impairment.
The positive effects of attending a preschool for a longer period might be explained by various educational, psychological and social factors. In general, the preschool setting encourages children to utilise and model socially appropriate behaviour and supports the development of various skills and competencies. The socialisation process in a preschool setting may help foster healthy child development. Socially disadvantaged children are far less likely to attend a preschool , yet are also at higher risk of suffering from developmental impairments. Since in our study children who had never attended preschool, 7.1% of the initial cohort, were excluded form the analysis, we may have underestimated rates of impairment. In our study only 1.7% of children had attended preschool for less than a year. Such a small sample size reduces the reliability of our findings. While our study found an association between duration of preschool attendance, we cannot be certain that this is a causal relationship due to the cross-sectional design of the study. For instance, it is conceivable that parents of more impaired children delay their entry into preschool. Shorter preschool attendance might represent a marker for an impaired state that prevents children from being enrolled. In practice, Public Health services, which are responsible for the enrollment of children in primary school and are accountable for the medical examination of all pre-school aged children, might be able to promote more accessibility of quality preschool experiences to children with social disadvantage through improving and emphasizing the recruitment process of children and parents from socially disadvantaged areas. More studies, especially those focusing on socially disadvantaged children are needed, in order to determine causative associations.
The location of a preschool seems to have a clear though less marked influence on impairments, when compared to duration of preschool attendance. Visiting a preschool in an urban region was associated with a higher risk for all the developmental deficits which we assessed. Of note is in our study rural children were significantly over represented, and that this may result in certain selection biases. To our knowledge, no previous studies have assessed the association between children's development and location of a preschool. We therefore have no other epidemiological data against which to compare our findings.
Other factors than longer duration and rural location of a preschool, so called protective factors, optimizing children's development and health are related to healthy eating, sports, social/family support and oral/dental hygiene . Preventive strategies targeting at young children can be implemented at an individual, community or national level.