Purpose: The aim of this study is to measure the effectiveness of the "Bug Investigators" pack in improving children's knowledge about micro-organisms, hygiene and antibiotics when it is used within the National Curriculum in junior schools. Design/methodology/approach: Teaching, using the "Bug Investigators" pack, was given by Gloucestershire primary school teachers. Children's general knowledge about hygiene, micro-organisms and antibiotics was measured by questionnaire before and after lessons using the pack. A sample of 198 children aged 10 and 11 years in eight primary schools completed the questionnaires before and after teaching. A focus group was held with teachers to explore their views after using the pack. Findings: Children's knowledge improved in all topic areas. Improved knowledge was most significant for what antibiotics do and how to use them and the value of our own good bugs (27, 31 and 16 percent improvement respectively). Knowledge about how bugs spread and hand hygiene was excellent (88 and 90 percent) before the education, but there was still 4 percent improvement in these topics. An exploratory discussion with teachers disclosed that some worksheets on viruses and resistant bacteria were too advanced for junior schools. Research limitations/implications: The study in this paper was undertaken in schools with relatively high-level four-science attainment, which could affect generalisability of findings. Originality/value: The "Bug Investigators" teaching pack was effective at improving knowledge about micro-organisms, hygiene and antibiotic use; it should be used more widely by junior schools. It is now a recognised teaching resource. Increased awareness of hygiene and prudent use of antibiotics should lower school absenteeism and improve antibiotic use in this generation of future adults. (Contains 4 tables.)