In elementary, i literally just sat with people in my class (cause i had to), in middle school, in 6th grade, i sat with a few people, that most likely pitied me. sometimes i sat alone. in 7th and 8th grade, i sat with friends i had. in 9th grade, for at least 2 or 3 months, i sat alone. then i told my counselor about it and she forced some 12th graders to sit with me until i found someone else to sit with. in the first half of 10th grade, when i still went to public school, i sat with a few friends i had.
in the second half of 10th grade all the way to 12th grade, when i transferred to an alternative private school, since my school was so small we didn't have a cafeteria, i sat with various classes in various grades. it was only about 6 or 7 people per grade so it wasn't that bad. i quite enjoyed it. i mostly sat with the 9th graders, or 11th graders. i miss it.
in college, now, i mostly sit alone in my art teacher's classroom whenever i can eat there, or i sit alone in the cafeteria. it's very lonely, but it's whatever.