Age is rated separately from the violation, so a young driver with one citation is often priced as nonstandard on age alone. The other difference is the family policy question, which affects the whole household rather than just you.
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Two surcharges stacking is the core of it. Carriers rate drivers under about twenty-five higher regardless of record, and a violation adds to that rather than replacing it. The result is that a twenty-year-old with one serious citation can price similarly to an older driver with several, which surprises families who expect a first offense to be treated gently. The second issue is structural. A filing against a parent policy is rated against every vehicle on it, so the household cost of keeping the student there can exceed a standalone policy in the student name. Both structures should be priced rather than assumed. A third point specific to students: a policy has to stay in force through summers and breaks, because a lapse during a proof period counts the same whether or not anybody was driving.