There are six academic departments at Preston International School each headed by its own Head of Department. All heads of department report directly to the Vice Principal (Academics) who is in charge of all academic activities in the school. The five departments are:
- Maths Department - consisting of Mathematics and Further Mathematics.
- ICT Department - Data Processing and Information & Communications Technology.
- Languages Department - English Language, Literature-in-English, Yoruba Language and French Language.
- Vocational Department - Basic Technology, Creative & Design Art, Technical Drawing, Music, Home Economics, Food and Nutrition, Physical Health Education, Design & Technology.
- Science Department - Basic Science, Physics, Chemistry, Biology, Agricultural Science and Animal Husbandry.
- Humanities Department - Social Studies, Religious Studies, Civic Education, Government, Geography and History.
- Business Studies Department - Business Studies, Economics, Accounting, Commerce and Office Practise.