The book contains all the necessary material for conducting a mathematical circle in grades 5-7 throughout the school year. Detailed topics for discussion in the class, sets of problems with solutions, mathematical games and contests are presented. The author - a teacher of mathematical circles with many years of experience - shares his professional skills in conducting a circle. The reader will find tips in the book on how to organize an lesson, present material and avoid typical mistakes. The book is addressed to teachers and leaders of mathematical circles. It will also be of interest to schoolchildren who are fond of mathematics and their parents.