We flew Airtran for the first time this past November. Seats for their flights are assigned when you "check in" to get your boarding pass. HOWEVER, you can do that on line 24 hours before your flight departs, by doing this you get your seat assignments at that time. By doing this 24 hours in advances you are almost assured of getting seats together. I haven't heard of any groups not getting seats together. You might be 3 & 3 or 2 & 4 for example if you had a party of 6 but you wouldn't end up with someone alone, or worse yet everyone sitting alone.
There is also some discrepancy about preassigned seating as opposed to choosing your own seats. My experience was when I "checked in" on line 24 hours in advance our seats seemed to be preselected in the sense I didn't get to choose where we sat. The seats were all together so it wasn't an issue for me. I understand that there is a way while on line to choose seats other than those than have been preselected for you, however, since I was happy with the seats we had I never looked into it further.
Airtran is different than Southwest. With Southwest you get a boarding letter and then everyone with that letter gets on at the same time in the order they got in line Group A, then B, then C. Southwest does let those who need assistance (including those with young children) board first so. Airtran gives you your seats so there is the "cattle call" boarding procedure that Southwest has. We've done both and have had good experiences with both.
I hope this hasnt' confused matters further.
