Despite being criticised for placing little emphasis on thinking, the majority of laboratory work at school level is taught "via" expository "recipe-style" labs. This has been seen to result in students struggling to be able to apply the practical techniques they have learnt in the classroom outside the narrow environment in which they were taught. This paper describes the design, trial and evaluation of a collection of ten practical activities which use a problem-based approach to laboratory instruction to deepen the students' understanding of the standard laboratory techniques they would be expected to know on entering an undergraduate chemistry laboratory. The practical activities have been trialled by over 100 students in eight different schools and feedback obtained "via" student questionnaire and informal comments provided by teachers. Compared to typical laboratory instruction, the students find the problem-based practical activities more interesting and better for making them think. Over 80% of the students indicate that the problem-based activities are "good" or "very good" for the application of practical techniques. Furthermore, the problem-based practical activities scored favourably compared to a typical laboratory activity for developing the students' independent study skills, team working and communication skills, scientific writing and research skills. (Contains 4 tables.)