Show the number of high schoolers for each grade.
SELECT grade ,  count(*) FROM Highschooler GROUP BY grade
SELECT grade ,  count(*) FROM Highschooler GROUP BY grade
[{'grade': 9, 'count(*)': 4}, {'grade': 10, 'count(*)': 4}, {'grade': 11, 'count(*)': 4}, {'grade': 12, 'count(*)': 4}]