US Visa Waiver coming back after 30 days? -

My son aged 19 heads back to the UK from the USA tomorrow, he was here in the US on the visa waiver program. I, his mum, am now living in the US and married a US citizen and Im in the process of applying for residency. My question is, my son wants to return for another three months in about three weeks time. We have looked at all the resources out there and we are still very confused if he can come back for another 90 days. BTW he does not want to move here full time.Any help would be appreciated -thanks in advance

There is no set time between visits. You will never find a government rule on this...it is up to the immigration officer. There is also no written rule about total time he may spend in the U.S. every year, but the unwritten rule is 6 months. In other words, a person cannot spend more time in the U.S. than in his own country. See site below.