<P> Classification is based on student body enrollment in grades 9--11) and used by the WIAA to maintain fair and equal competition between its member high schools . The organization places member schools into one of six tiered classifications based on enrollment ranges: 1B, 2B, 1A, 2A, 3A, and 4A . The enrollment ranges are evaluated by the WIAA Executive Board biennially and finalized for a two - year period . Enrollments of single - gender schools are doubled for classification purposes . </P> <P> Current classifications for years 2016 through 2020, as approved by the WIAA Executive Board on January 25, 2016, were: </P> <Table> <Tr> <Th> Classification </Th> <Th> Enrollment (gr. 9--11) </Th> <Th> Average per class year </Th> <Th> Member schools </Th> <Th> Opted - up </Th> </Tr> <Tr> <Td> 4A </Td> <Td> 1343.29 + </Td> <Td> 447 + </Td> <Td> 64 </Td> <Td> 22 </Td> </Tr> <Tr> <Td> 3A </Td> <Td> 971.72 - 1343.28 </Td> <Td> 323--447 </Td> <Td> 66 </Td> <Td> 13 </Td> </Tr> <Tr> <Td> 2A </Td> <Td> 461.25--971.71 </Td> <Td> 153--323 </Td> <Td> 65 </Td> <Td> </Td> </Tr> <Tr> <Td> 1A </Td> <Td> 214.5--461.24 </Td> <Td> 71--153 </Td> <Td> 65 </Td> <Td> 8 </Td> </Tr> <Tr> <Td> 2B </Td> <Td> 83 - 214.49 </Td> <Td> 28--71 </Td> <Td> 40 </Td> <Td> </Td> </Tr> <Tr> <Td> 1B </Td> <Td> 26--82.99 </Td> <Td> 8--28 </Td> <Td> 64 </Td> <Td>--</Td> </Tr> <Tr> <Td> Total </Td> <Td_colspan="2"> </Td> <Td> 384 </Td> <Td> 48 </Td> </Tr> </Table> <Tr> <Th> Classification </Th> <Th> Enrollment (gr. 9--11) </Th> <Th> Average per class year </Th> <Th> Member schools </Th> <Th> Opted - up </Th> </Tr>

What is the difference between a 3a and 4a school
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