alot or a lot?

'A lot' seems to be one of the most confusing expressions for younger students. While 'alot' is never right, 'a lot' should be avoided altogether. So why make up an expression that's not appropriate to use? I don't know. In any case, 'a lot' can render the sentence ambiguous; "It rain a lot in September." Does it mean that the volume of rain is high or that it rains often? To avoid the ambiguity, 'very much' or 'often' should be used.