You can easily obtain an EIN from the IRS and this can be done over the phone, online, or by mail. You might find over the phone easiest. Then if you have any doubts about a field, you can ask.
It's smart to use an EIN (and not someone's social security number) for your bank account. This is an important first step. Just be aware that ALL this does is give you a tax ID reference number. By itself, this has nothing to do with whether or not your organization is tax exempt or considered a charitable organization.
When the account was set up I was just starting my first year in the PTA, so I just smiled and nodded and signed where I was told to.
This year I came back to the PTA after 2 years off and since I was the only one with any PTA experience I was able to look into some things I'd always had questions about; not only were we using the school's EIN, we were using their tax exempt number as well, even though we had our own. Now we have a new bank account using all of the proper numbers and I feel better.
Using the school's EIN was common in the past. But as accounting rules have formalized and liability (for everything!) skyrocketed, most districts have cracked down on this practice.
Actually, it was probably never "right" to do this, but I think a lot has changed over the last 10-15 years with the growth of the Internet and the fact that IRS rules and state laws and such are easier for everyone to research and understand. As awareness of proper procedure grows, the policies formalize even more.
No one should use the school's EIN except for persons officially authorized to act as agents of the school. Everytime the EIN is used, the school is responsible that the transaction meets all federal, state, local laws as well as it's own policies.
That being said, if this is still commonly accepted practice in your area -that's up to your district. But once you start asking questions, the lawyers and purchasers and risk managers will quickly say, "No Way!".
Note - since you are a PTA, I am surprised it was set up this way. PTAs are typically independent and have their own EINs.
Our PTA had our bank account under the school's EIN number as well, something we changed this year. I contacted our county PTA and they were able to give us the EIN number easily, plus they emphasized that we were NOT to use the school's number. If your county PTA can't give you the right number then I'd contact your state PTA.
Since we are not a school sanctioned club they will absolutely not allow us to use their EIN. the principal is very active in our group and helpful but this was not allowed by the district