If you can't get the College Board to encrypt to each of these user's public key, you do have the option of using one key for each of them.
One user can generate a new key on his/her machine.
Although you don't have to do this step, you may want to. Right click on the key in All Keys, select Properties, and use the Add Email Address option on the top left, to add the name and email address of each of the other users. This would result in having a key that all email to each of those email addresses by the College Board would be encrypted to.
Right click on the completed key, select Export. Before you select Save, select the option to the lower left of Include Private Key. Then take the exported key to each of the other user's machines, and double click on it to import it. After importing it, each user should right click on the key, select Properties, and set Trust to Implicit.
For decryption, each user will need to have the key's passphrase. But each user can then change the passphrase to what ever they want.
Of course you will need to send the key to the College Board for their use. You will need to do another export of the key for this, and in this export make sure that you do NOT include the private key.