The Legend of Memo Castillo (the Kids in Mrs. Z's Class #4) - William Alexander - Bog

"Guillermo 'Memo' Castillo and Theo Chang have been best friends since they were in kindergarten, and now they're partners in Sorcery, too--the mega-popular collectible card game, that is. Memo and Theo are excited to attend the upcoming science fiction & fantasy fan convention not far from Peppermint Falls. They plan to dress up in costumes, play in their first-ever Sorcery competition, defeat that arrogant fifth grader Josh Harkan in the tournament, and have an awesome day. But Memo's dad can't drive them to the convention. His mom can't, either. Theo's family is out as well. That leaves just one option: Memo's fearsome abuela"--