This article reports the development and refinement of science and mathematics integrated activities for middle school students. The expectations of the National Council of Teachers of Mathematics that students develop an understanding of mathematics and an ability to apply it gave birth to these activities. The expectations of the National Science Education Standards that students engage in inquiry and discussion, as well as assessments that encourage them to analyse their findings and organize their conclusions, also framed these activities. Three middle school science teachers, who were less than confident in their mathematical abilities, piloted 3 of the 24 activities. Classroom discourse and teacher feedback were used to refine them. Diverse attitudes regarding the usefulness of mathematics and the comprehensive benefits of integrating mathematics into science activities are reported. Key components of the activities include detailed instructions, resources and references, discussion questions and assessment suggestions. Cooperative learning is highlighted as instrumental in the comprehension of both mathematics and science.