ML, the workability of homeschooling as a plot device depends on what you mean by missing school. If you just mean that the child wasn't there for a couple of years and so missed whatever events happened at the school during that time, you could use homeschooling, illness, travel, temporary job transfer of a parent, temporary custody transfer of the child (went to live with Grandma for a couple of years), study abroad (depending on the age of the child). If you mean that the child is two years behind in their schooling (i.e. a 12-year old in fifth grade), then homeschooling is not your answer. A child who left school after third grade and homeschooled for two years would return to school in the sixth grade, not in the fourth.
An illness which would make a child fall that far behind in school would have to be so serious that the child couldn't study, even with a private tutor. A hardship situation might work--say, the family is in such dire straights that they are traveling from town to town following odd jobs (maybe migrant farm workers) and the parents keep the child out of school in order to stay off the Child Services radar screen for fear of the child being taken from them or because they need the child to work or scrounge. BTW, it is illegal to pull a school-aged child out of school to work. It's grounds for removal to foster care.
