I found the answer to my question, along with reams of WDW information:
Highest Attendance:
Presidents' week in February
Mid-March through Late April (Spring Break)
Memorial Day weekend
Mid-June through Labor Day
Thanksgiving Day and weekend
Christmas week through New Year's Day
Moderate Attendance:
After Presidents' week in February through early March
Late April through early June (except Memorial Day weekend)
The first part of Thanksgiving week
Lowest Attendance:
January (except New Year's Day) until just prior to Presidents' week in February
The week following Labor Day until just prior to Thanksgiving week
The week following Thanksgiving until the week prior to Christmas
Highest Attendance:
Presidents' week in February
Mid-March through Late April (Spring Break)
Memorial Day weekend
Mid-June through Labor Day
Thanksgiving Day and weekend
Christmas week through New Year's Day
Moderate Attendance:
After Presidents' week in February through early March
Late April through early June (except Memorial Day weekend)
The first part of Thanksgiving week
Lowest Attendance:
January (except New Year's Day) until just prior to Presidents' week in February
The week following Labor Day until just prior to Thanksgiving week
The week following Thanksgiving until the week prior to Christmas