"For" in this instance means "for the benefit of". "Record" in this instance means "a list of adventures". It is not a good record, of course, because the boy was misbehaving. However, other children will be impressed by what he did. Thus, the sentence means: "He has surely created a list of adventures for the benefit (because it helps them to dream) of thousands of children who dream of evading school.

IMO, it directly connects two parts of a sentence with extra emphasis. The boy set a new record, particularly to the children who also dream of evading school. Not so important to anyone else. The emphasis is the new record is most important to the children.

to set a record for it means thousands of children will follow his path