In Tennessee, line judges are required. The R1 and R2 are assigned through an assignor. The school is responsible for line judges, score keep, score board operator and tracker. My association will supply line judges (certified officials) if requested for regular season and are required for sub-state and state tournament.
Adult line judges are preferred, but I have had varsity players call JV matches. Over all, the kids do a better job than the adults. (they play club) many of the adults have several kids play and have many years experience line judging and are very good.....And some are 1st time don't know which end of the flag to hold. You just work with them. I have ref'd for 13 years and have only had one line judge that had to be replaced.
And yes, some of the worst line judges are officials.
There is no cost to the school to provide an adult line judge. Usually, the varsity parents call for the JV match and the JV parents call for the varsity match. I have recruited some to become officials.
In 13 years, I have ref'd over 1000 matches, but not one without a line judge. You can always over rule a line judge, even a good one.