Going to college is a common expression, which means "continuing (studying) and entering the university", that is, the purpose of "continuing" is to enter the university. Go on college is an informal expression, which means "continue to study in university". In fact, there are few examples of going to college mentioned by British and American people. If someone really says this, it's because go on is synonymous with carry on and keep on, both of which mean to continue. But the verbs in carry on and keep on are transitive verbs and on is an adverb (not a preposition! ), but go in go on is an intransitive verb Although they have the same meaning, they are used in different ways and cannot be used interchangeably in many cases. For example, it is common to go to college and continue, but no one will say to go to college and continue. If you use go on, people will say go to college and go on.