Back to School Several titles will let kids put on their thinking caps. An addition to the Kaleidoscope Kids series, Who Really Discovered America? Unraveling the Mystery & Solving the Puzzle by Avery Hart, with b&w cartoon illustrations by Michael Kline, challenges readers to partake in activities and experiments that will help them get to the truth. Theories, biographies and sections called "Think about it," sprinkled throughout the volume, raise a series of provocative questions. (Williamson, $10.95 paper 96p ages 7-14 ISBN 1-885593-46-5; Aug.)

In her historical activity book, Marco Polo for Kids: His Marvelous Journey to China, 21 Activities, Janis Herbert chronicles the famous explorer's travels along the "Silk Road" to the palace of the Kublai Khan. Projects feature the various cultures that he experienced. For example, kids can make a mandala (a Tibetan circular sand painting that symbolizes the circle of life) and play "Eagle and Chicks," a Chinese game. Archival artwork and prints add to the handsome volume. (Chicago Review, $16.95 paper 129p ages 9-up ISBN 1-55652-377-7; Sept.)

Diane Stanley's Time-Traveling Twins head for a second adventure in Joining the Boston Tea Party, illus. by Holly Berry. The date is 1773, and Liz, Lenny and Grandma hear Sam Adams speak and join the "Mohawks" in dumping tea into the Boston Harbor. Inviting illustrations as well as word balloons filled with humor ("I always thought tea came in little bags!") and information ("Women won't get to vote until 1920") should pull in aspiring historians. (HarperCollins/Cotler, $15.95 48p ages 5-10 ISBN 0-06-027067-5; Aug.)

For those heading back to preschool and kindergarten, Sam's Big Book of Words by Yves Got features the busy bunny exploring the world around him. Each spread focuses on a heading (such as "The Aquarium" and "Sam's Family") and includes clearly labeled everyday objects and people (books, sun, baby-sitter). (Chronicle, $12.95 32p ages 2-6 ISBN 0-8118-3088-8; July)

With 35,000 entries, 1,100 color photographs and a reference section including a thesaurus and maps of the world, the Macmillan Dictionary for Children—4 th Revised Edition makes a handy resource. Other features include spelling hints, brief etymologies for selected words, and expanded illustrations with labeled parts. (S&S, $16.95 912p ages 8-12 ISBN 0-689-84323-2; July)

Younger children can build their vocabulary with First School Dictionary, illus. by Stephanie Strickland and Sebastian Quigley. Each page features drawings and photographs and a vertical listing of the complete alphabet on the side. A section at the end offers lists of frequently used words, pronouns, etc. (Barron's, $13.95 184p ages 5-8 ISBN 0-7641-5434-6; Aug.)