I would go. I'm not saying that your son is doing this, but at the college where I work, I have seen students go to great extremes to hide the problems they have got at college from their parents. For example, in the past students have deleted messages left on answerphones, given wrong parental contact numbers, destroyed letters sent home to parents and so on.... It happens enough that it is now policy that when letters (expressing concern about students) are sent home, they are handwritten and sent in different envelopes with stamps on and not franked in a bid to disguise them! Yet still we find some students manage to intercept them. In my experience, some students are capable of managing their own learning at 16, but many are not... and there is no way of knowing unless you go to parents' evening and find out!
Also, interestingly, I find that the students who often struggle most with the adjustment at college are those who sailed through school with a string of As and Bs. It's those students who manage to get good grades at GCSE without much work or effort put in, who think that they can carry this on at 'A' level, and of course they can't. It's not always the students who you might think it would be.
Also, whilst I'm on this, another issue we sometimes have with students who go the other way and do waaay too much work and end up getting stressed about it. Sometimes it is good to talk to the students together with their parents together to tell them they need to relax a bit, cause some students can go totally OTT with their studying. Only this week, I've had a girl in tears in class because she has been taking on far too much and putting way too much pressure on herself. It is good for the students to hear these messages both at college and at home.
I've got parents' evening at my college next week, and I will be having both conversations - with bright students who think they can coast, and who need to be told that they are underachieving, but also the OTT students who need to be told to pace themselves if they don't want to burn out. But the key thing is you'll only know if there are any issues if you go.
Also, you say that it's only the first term, but given that they take their exams in May, certainly by Christmas I am half way through the teaching content of my course. I will have finished teaching by April and revision starts then, so now is the time to do parents' evening if you want to nip any issues in the bud.
HTH