I didn't realise how many kids got to age 16 without learning to tell the time until my first job in a school, including more able kids admitting that they were worried about their exams because they wouldn't know how much time they had to complete questions - unless there was a digital clock visible at the front.
They've just not needed to know - they've been got up, taken to school, they're told when to come in from playtime/lunch/break, they stay until they're told they can leave, they're taken home again. And then when they're older, they've followed somebody else who seems to know what the piece of paper means to get to lessons/they've been told to go to the next one by staff or the pips have signalled the changeover.
Add into that finding their own way around areas where they might not have been before or have only ever travelled by the car route/never caught a bus in their life, they've never had to read a timetable, move around school without a teacher chivvying them along, tie a tie, do up shoelaces, get changed in a hurry - and many more than you expect do struggle.
It is utter bollocks that DSS wasn't ever taught the days of the week or how to tell time - but he may have been absent or not engaging in it when they were taught. Especially if he happened to be absent or not engaging some time around Year 5 when teachers tend to try to pick up the last few who aren't 100% certain. It is however believable that he's unable to make himself food or drink, pick up after himself or suchlike, as a mixture of mornings where two pints of water gets tipped over the countertop and floor or glasses are dropped/drinks kicked across the carpet makes it possible that a harassed parent will say 'give it here, I'll do it' and never gets around to making them do it for themselves.
In any case, that's perfect for;
'I never got taught how to do that'
'Well, now's the perfect time to learn, then. Come on'.
Most kids do learn very quickly when they have to - some will struggle or resist, and some will be noticed and flagged up by staff for potential assessment/support. It's the reason why many secondaries have a 'nuture group' or form where more children have SEN, EHCPs or a gentler transition.
Of course, this year, it's likely that the transition will be gentler than the usual in at the deep end, as bubbles mean many are having almost all their lesssons in one room and they're kept largely separate from the other years for breaks and lunches. And we're aware that they are understandably more vulnerable, nervous, etc, so they're going to have more support than usual.
DSS might have dyspraxia or dyslexia, he might be babied too much, he might have learned helplessness. Encouraging him to do things in a chirpy way means that the ones he will be able to do are covered and shows the ones he can't or won't get his head or limbs/digits around. And you aren't the wicked stepmother, you've engaged with him doing something for himself/taught him a new skill/found out that he genuinely cannot manage something. All of which are good, compared to a conversation along the lines of 'there's something wrong with that child/you've spoiled him/he's lazy', which are all going to lead to huge blow ups.