Why is writing "alot" such a common mistake?

Why is it such a common mistake (particularly among school-children) to connect certain pairs of separate words? The most obvious example probably being:

e.g. "a lot"->"alot"

Is it because- in this particular case at least- there is already a valid word "allot" that exists?

Maybe also, it helps that "a" is a valid prefix to a word (e.g. "a-plenty").

Solution 1:

Possibly people have a natural tendency to spell "alot" in a single word because the brain processes it as a single word. At any rate, with its use for quantification, it clearly has some "special" properties. Notice the difference in verb agreement between:

A lot of the problems are due to bad planning.

A lot from the auctions is missing.

This taken with the fact that "a lot" can be used adverbially ("he got a lot further") probably make it "feel" like a single item in terms of how the brain processes it. The perceived "obligation" to spell it as two words, like any spelling, is just an arbitrary convention.

A five-year-old child learning to write may not have even come across the word "lot" outside the phrase "a lot of", and occasional phrases such as "a whole lot of" which split "a" and "lot" are rare compared to the basic phrase.

Solution 2:

As usual, there’s a certain logic to this common mistake.

Of course if you have read and learned the spelling, it makes sense the way you’ve learned it. But imagine for a second that you weren’t really the reading type, and you didn’t know how a lot was spelled. Would you think of it as two words?

Consider We care a lot. Is lot a noun there? How many other nouns can do that? We care a bicycle? We care a friendship? I could accept We care a bunch / a bit / a little, and a few temporal expressions like We care this year / all the time, but a million other nouns don’t work. So it’s no wonder some people put a lot in the same mental bucket as sometimes, occasionally, and deeply.

Also— a lot is an idiom. It does not mean the same thing in the everyday We have a lot as it does in the more literal We have a lot in the Appalachians where we’re going to build a cabin someday. There is a pattern in English that such idioms tend to get fused into single words: all ready/already, all most/almost, a wake/awake, a way/away, and a live/alive. This also explains why alright is so common.

Of course the standard spelling has its own logic: a lot of bananas is a typical noun phrase whereas alot of bananas would be pretty odd; the lot of them and the whole lot are occasionally heard; and so on. But you can see how someone might make the mistake.

Solution 3:

I think it's simply a misspelling. In the case of "a lot", it's a term that's frequently used, and it might seem like one word when pronounced. So I'm thinking that until told differently, kids think that "a lot" is one word.

Solution 4:

I can't post images in comments, but I think this one is worth a tenth of a myriad’s words:

So: no, it's not “on its way to becoming a recognised single word”.

^{And most of the hits from this ngram are not actual uses of “alot” in the context we are discussing here, but OCR issues or names of foreign places.}