Leigh Botts describes himself as being in the middle of the spectrum, implying he considers himself average or moderate in personality or traits. He humorously refers to himself as "the mediumest boy in the class," highlighting his mediocrity or unremarkable presence among his peers.
He uses this humorous self-description to convey a sense of humility or self-awareness. The quote from Beverly Cleary's book "Dear Mr. Henshaw" showcases Leigh's modesty and his attempt to position himself as neither extraordinary nor insignificant in his social environment.