This would have been a 7 out of 5 stars if it weren't for the gift shop. See more below.
The staff at Space Center Houston are wonderful. From the minute you enter, the staff (even those standing in the sun!) are welcoming and informative. They try to get you through the line as fast as possible. I wish they had an option to skip the photo line, but I understand they are trying to make money.
Inside the Space Center, there are plenty of people ready and excited to assist. I recommend taking the tram tours first. It gets hot during the day, and the tours tend to fill up.
After lunch (which is mediocre), take in a movie while relaxing in one of the amazing theaters or enjoy a live presentation. Don't accidentally skip the opportunity to touch the moon or go through the rocket.
The last stop is always the gift shop. Be warned- this is not where polite and helpful employees can be found. I have had several encounters with employees being rude to young people in the store. I don't know if this is for all students or only the Black and Brown students that I work with, but employees regularly speak harshly, refuse entry, make them put their bags down before entering (which is not a policy enforced for all), and overall make them feel unwelcome. Unfortunately, this has been my experience on more than one visit with more than one employee.
Educators- ask about the discount in the gift shop. It is inconsistent, but sometimes you can get a bit off of your purchase!