Sadly with laptops you get what you pay for (I just shelled out 500 quid on a new one).
The thing that jumps out at me with that Acer laptop is the i3 processor, which is going to be slow. Even if you don't need high end specs (usually for gaming) you want a good enough processor that you can, for e.g., have maybe word, powerpoint and a browser open simultaneously. And chances are an i3 is going to make that feel like wading through treacle.
Quick guide to making sense of technical specs:
RAM - think of it by analogy with planning some sort of project longhand. RAM is the equivalent of what size sheet of paper you have. 4GB would be like trying to plan something complicated on a post-it note, 8GB gets you a decent sized sheet of A4, etc. The processor speed tells you how fast the chip can do the actual activities you want it to (complicated sums on an excel spreadsheet, rendering graphics in real time in a computer game, coping with more than one task at once if you have more than one window open). Then there's all sorts of other features of useability - screen quality (if you want to watch Netflix on it), how many ports it's got to connect to other devices (if you want to get photos off your phone and onto your laptop), etc.
My list of technical specs for you would be:
half-way decent chip (Intel i5 or equivalent)
enough RAM - 8GB is probably about right without pricing yourself out of the market (16 GB would be nice, 4 GB probably too limited).
enough ports - at least two USB A ports would be an absolute minimum, I'd say.
Decent screen quality.
www.techradar.com/uk/news/the-best-laptop-deals is a useful article with recent reviews.
I think your school is right to insist on a laptop rather than a Chromebook. DS has a Chromebook his granddad bought in a fit of enthusiasm, and to be honest, it's so incredibly limited in what it can do that I absolutely hate it.
With Currys it may well be that what you see on their website simply isn't available near where you live. I physically went into our local branch (having decided on budget and decided roughly what I wanted). They didn't have any of the versions I was after, but did manage to source a very similar one in the town 45 minutes drive away (Ryzen 5 chip rather than Intel i5 - pretty much do the same job). The saleswoman (who was very clued up and very helpful) said part of the problem is their supplies have been absolutely stripped down during lockdown (they were reduced to getting stuff out of the stockrooms of their physical shops in order to supply online orders) and the replacement stock hasn't come in yet).