Hi Weymon,
depending of your configuration this can happen.
Remember: A WLAN is a shared media liak a hub was in the past. Th AP is able to handle round about 22 Mbit at a maximum. If you have configured 2 Mbit as minimum speed the 12th client "bombs out" the capabilities of the lab.
So for 29 Workstations you will need at a minimum 2 APs and - if you configure some minimum speed above 1 Mbit - you will need 3 or more APs.
Good Luck,
Frank