Heavy-handed tactics used to side-step procedural safeguards are typical of toooo many school districts.
From personal experience I can tell you the sd's most probable position would be that the IEP/ARD meeting held without you and husband was a "staffing"; the IEP will be deemed a "draft." Without hard proof to the contrary, you loose at Due Process.
You'd need an experienced special education attorney to win at Due Process in my opinion.
Special Education attorneys that will take a case from a parent are hard to find in southeast Texas. When I was looking for one, I found one in the Houston area. School districts had the remainder on retainers. If you want to go that route, PM me and I can put you in contact with an advocate in the Houston area that has the attorney's name and number -- you might can network that way and find a sp ed attorney in your area. If you live near the Houston area, you might want to contact the advocate anyway.
Another tactic used is the "attendance/sign-in sheet." I've been to ARD's in different school district's in SE Texas, and they want everyone to sign the "attendance sheet" first thing. It's not an attendance sheet per se -- it's the last page of the IEP form, and parents inadvertently sign it signifying their agreement to the IEP which hasn't even been developed. Therefore, I advise the parent(s) to sign it in the margin (outside the signature boxes) with the notation signed to acknowledge parent attendance at the ARD meeting only.
I don't know if this is the case with-your sd, but I wanted to alert you to it so that you understand the need to act quickly.
Even if you didn't sign that type "attendance sheet," you have a short period of time to either notify the sd you are requesting mediation or filing Due Process. (Use Certified Mail)
When parents and sds disagree at an ARD, the ARD meeting reconvenes within 10 days. During the interim, parents (and sds) should be gathering additional information to support their positions.
I also recommend that before the sd's recommendation is dismissed out-of-hand, that you and husband visit the facility, classroom(s), meet staff and teacher(s), ask lots of questions. It could be that their recommendation is a good placement and the dates for working out the transfer can be negotiated.
You might leave the facility knowing it is not the appropriate placement for your son, however, you may get a better idea of what would be benefical for your son (perhaps some of what you learn there can be incorporated into his IEP at his present school, maybe look for a different facility that does X,Y, Z but not A, B, C?)
At the very least, while answering a Complaint or presenting evidence at Due Process, you wouldn't want to give the sd ammo such as:
No, they didn't even bother to ask to see the facility; no they didn't...., etc., etc.