This is pulled directly from the Board of Directors minutes, regarding the rule.
19-3.2 First Time Transfer Between Member Schools
a. Students who transfer between Member Schools for the first time during the first six (6) semesters after their initial high school enrollment will have full eligibility, provided: (1.)The transfer occurs on or before the Start of Practice Date of the sports season in which the transfer occurs; and (2.)The transfer is not the result of undue influence (rules 20-1 and 20-2, past link).
b. Students who transfer during the first six (6) semesters, having had the opportunity to participate in three (3) seasons of eligibility of a sport, will be subject to a Thirty (30) day non-competition period or half (1/2) the Maximum Number of Contests, whichever is less, in each sport in which they participated during or after their third year of eligibility, during the Three-hundred Sixty-five (365) days preceding the transfer.