There are two main uses of the apostrophe: (1) omissions, showing where letters have been missed out, such as can't, (2) possessives, such as boy's. The first type of apostrophe can be useful to avoid confusions between words such as can't (cannot) and cant (what many educational reports are full of). The second shows the old form of the possessive (Chaucer wrote "at his beddes heed" meaning "at the head of his bed"). If it is singular, the apostrophe comes before the "s" (boy's confusion - one boy is confused), if plural, after it (boys' confusion - many are confused). I ask children "Who (or what) does it belong to?" Then I get them to draw a box round the person or thing it belongs to, for example, boy or boys. So one answer for Andrew might be that we could probably do without some apostrophes, but others are useful, as well as correct, so he does need to learn them.