Not too sure if intelligence is hereditary, it's not unheard of for kids from working class backgrounds to go to university, you know...
It's more about educational and creative stimulation children receive, which is vital in developing their intelligence, probably. If a baby plays lots of games as a child that improved his mind, he'd probably have developed greater than a kid who had little stimulation, he'd then go on to read more, have greater attention span, etc. This probably has some role in determining their memory span, educational capabilities, how he learned information and so forth. That said personality is a massive factor, some from poorer class backgrounds approach education with a similar attitude to their parents and some don't. And also, university degrees aren't entirely synonymous with intelligence, you know. My mother and my auntie (the latter had the highest IQ in her school) didn't get degrees because they came from a very working class backgrounds, it just wasn't an option-they had to get out and work. (which is, er, why EMA is was a god sent.