Table 1 The contents of four interventions

The first intervention

To cultivate the awareness and willingness of participants about Internet use behaviors

(1) Health education courses

Implement: Health education courses were conducted in class units and were taught by trained teachers who majored in health education. Each course lasted for 45 min for every class in every intervention. It was carried out by a combination of teacher teaching, videoes and scenario simulation. The courseware used in this intervention was copied to the school teachers, and they repeated the intervention contents to the participants in the daily class meetings.

Contents: The main contents embraced publicizing the harms caused by excessive Internet use and the benefits of reducing Internet use time, with the objective of promoting the action self-efficacy about Internet use behaviors.

Risk perception

Outcome expectancy

Action self-efficacy

(2) Customized manuals

Implement: The manuals were uniformly produced by the research team and distributed to all participants after the health education courses.

Contents: The main contents were similar to the content of the health education courses, including the harms caused by excessive Internet use, the benefits of reducing Internet use time, and the correct approaches to surf online.

The second intervention

To consolidate the effect of the first intervention and to promote the formation of the intention.

Health education courses

Implement: The implementation method was the same as the first intervention.

Contents: The content emphasized and deepened the content of the first time.

Risk perception

Outcome expectancy

Action self-efficacy

Intention

The third intervention

To help participants formulating plans.

(1) Health education courses

Implement: The implementation method was the same as the first intervention.

Contents: The main contents were how to make plans to help the participants to turn their intention into actual behaviors, including the duration, the implementation of the plan, etc.

Planning

(2) Guidance on plan formulation

Implement: After the health education courses, one-to-one guidance was provided for the participants by the trained teachers.

Contents: The guidance content was about clarifying the plan’s objectives, implementation methods, duration, possible obstacles, obstacle solutions, etc.

The fourth intervention

To strengthen the maintenance self-efficacy and reduce the online time.

(1) Health education courses

Implement: The implementation method was the same as the first intervention.

Contents: The main contents were the introduction of specific cases (including successful cases and failure cases of reducing online time) and analysis of the reasons for success or failure.

Maintenance self-efficacy

(2) Provide physical exercise equipment

Provided freely table tennis rackets, skipping ropes, and other sports equipment to every class.

Internet use behaviors