Lester's father was an astronaut who was killed during a mission, so he has been raised and home schooled by his mother. When his mother gets a job at the local public library, Lester is thrilled because he loves to spend time there, but she tells him that instead, he will have to go to school. Lester has a lot of trouble with this-- he gets hungry and is not allowed a snack, he can't study what he wants when he wants to, noises overwhelm him, and the other children, picking up on his odd behavior, are mean to him. There is one girl, Abby Chin, who is friendly to him and tries to help him navigate the difficult waters of fifth grade. Abby had won the science fair the year before, and Lester is very excited about the fair, especially when his mother finally gives him permission to do a flight themed project instead of one on plants. When a new girl arrives and Abby starts to hang out with her, Lester's behavior becomes more erratic. Luckily, the school tests him and finally delivers a diagnosis so that Lester can get the help and support that he needs.
It seemed unlikely that Lester's mother would not have figured out that he was on the autism spectrum before he started school, but this has certainly happened before. It was much more common fifteen years ago, but since Lester was home schooled, it makes sense that his mother might not have had a wider range of experience with children's behavior.
This will be good to use with Baskin's Anything but Typical and other titles with characters who are on the autism spectrum. There are a number of good books on this topic, including Choldenko's Al Capone Does My Shirts, Dowd's The London Eye Mystery, Lord's Rules, Mackel's The Silence of Murder and McGovern's Chester and Gus.