Seriously! No parental controls for U-verse internet?

If only I knew what “cascade” behind the gateway meant. I bought a wireless modem but not sure how to install it on the gateway. 

Google search is your friend.  Best bet is to search within these forums first and then expand out.  While you can use the search in the search box at the top of this page I prefer to use google.  Just add the phrase site:forums.att.com  to the google search to limit searches to just these forums.  For example look for things like "connecting modem behind gateway".  Unfortunately some of the details vary from gateway to gateway.  So you should post which gateway model you are using and which router you bought.  Perhaps someone whose done it for those models will reply in this thread.  I can't help you with this since I am not a router expert and have had no need to place the gateway in pass through for another router behind it.

Can't tell you how many posts I have seen requesting this  and Comcast has had it (built-in! NOT a klugey work-around) for over  a year now.  Half the replies I see say "Not everyone want this so if you do, go buy and set-up/daisy-chain a different  router", but AT&T needs to realize that, although it's not their WHOLE customer base, it's a significant portion that is interested in this and they want a cookie-cutter all-in-one solution, not another project to work through, especially for those  that are not technically savvy.  AT&T, please prioritize this feature or  risk  losing customers... this  functionality is VERY important to those of us that want it...

Just something else that spectrum has that att doesn't have. How did they become #1 in customer satisfaction? 🤔

Sorry AT&T that’s not a solution it’s a punt right back to your customer base.   Keep up w the competition and the real challlenges to survive in this market.   Do we really need to buy, connect, configure and maintain another device ?