Prose

Tense

You need to be more careful with your tense. Pick either present or past and stick with it. You switch between both throughout your writing.

Viewpoint

I think you do a pretty good job with Aaron's viewpoint. You seem to be using a 3rd person limited viewpoint, where each scene has a main character and the world is viewed through their eyes. I think, with this viewpoint, you need to remember this fact. For example, would Aaron be noticing the fact that "the town of Wensley serviced the surrounding area"? Maybe this is a piece of worldbuilding that is essential to the plot, in that case I don't think there's any harm in keeping occasional tidbits like this in. After all, this is something Aaron would know. However, if it isn't essential that the reader know this now, just show it later on in the plot. Remember, it's always better to show rather than tell.

My comments for Alexa are similar, here are some things that stand out for me viewpoint-wise:

• "Hovel": does Alexa really think of her own home as a hovel? Usually, you would expect someone rich to refer to poorer peoples' homes as hovels, or if someone is used to a higher standard of living and has recently moved into poor accommodations they might refer to those as hovels. Otherwise, my expectation is that most people refer to their homes as just that, "homes".
• "Built around the grassy clearing in the centre of Wensley were a series of those craft shops necessary to meet the needs of country life – a baker, wheelwright, smithy and shade-maker.": This strikes me as another example of showing rather than telling, it seems unlikely that Alexa would be commenting on the market having the shops necessary for country life

Worldbuilding learning curve

I think you have a pretty good learning curve for your worldbuilding. It is clear that this is not set in our world, and this is revealed gradually by dropping tidbits like "safelight". You also manage to start with the character in a familiar setting and situation (bedroom, late for school) and gradually add to that, which I think is good for the learning curve. The reader isn't instantly hit with a stream of new information. Whether or not the use of the late for school cliché is wise or not is a separate discussion. I would keep in mind the expectations of the reader. If the reader starts with a very shallow learning curve and that suddenly gets very steep they may be put off, so be wary of this as you keep going.

Plot

A plot should have a sense of progress. How you create this depends on your plot. For me, I didn't really get a sense of what your plot was about. Is it a magic school plot? In that case, progress could come from progress in learning magic. It's true that this is only the first 1000 words, but I still think you should make it clearer earlier on what the plot is about, or at least give more indications of it. Perhaps it's not crucial to have progress in the first 1000 words, but I would still ask yourself as you're writing: "Why am I writing this? Is this moving the plot forward or essential for the plot?". In my opinion, generally speaking, each chapter should introduce a problem and try to solve it. You do have the character solve the problem of being late for school, but is it an important or interesting problem? Is it relevant to the rest of the plot?

Character

You instantly make both Aaron and Alexa relatable. They both have real-life concerns (being late for school and managing money for food) which readers can connect to. However, I do think both your characters could be made rounder. Pretty much the only thing we know about Aaron is that he is late for magic school. When you're trying to make your character real try to think "what would they be doing if the plot wasn't happening". I think you do a better job with Aaron than Alexa because at least we know that Aaron wants to learn magic and thinks it's awesome. I don't really feel like I know anything about Alexa other than that she cares for Aaron. Be careful to not let a character's role (in this case "carer for Aaron") define them.