You have to keep at it on all fronts. Emails via school, direct asks by parents when you see them at other school/sport functions, get your scout to give you a list of his friends he wants to have in scouting, contact parents directly and find families in the younger grades. You also recruite the kindergartner parents during the year. It takes several times to get people to a Join Night. But then you are NOT done. You keep Recruiting. ALL YEAR.
I have been out of the Pack 3 years now, and I am still recruiting for them and others.