I did a page speed test and the speed of this page: https://cestarhighschool.com/ is very low in the mobile. I am planning to implement AMP to improve the speed. Does it actually work? Is there anything else I can do to improve the page speed in mobile?
I'd say you need to optimise the entire site before thinking amp is the solution to your problems. I had the loading wheel on my desktop and I'm on an 80Mbps line so I'd hate to think what it's like on 3G mobile.
AMP will not help. AMP allow google to cache news stories on their server so they can be displayed when someone searches for that news. Implementing AMP on your site just allows Google to extract the data, it doesn't make you site any faster.
If you want a faster site you first need to sort out your hosting. Time to first byte isn't good. Use gzip and caching and see if there are any weird redirections.
I'd also consider using a different theme. Bootstrap is now very dated and clunky and there are a whole bunch of scripts and styles slowing things down. But the main culprit seems to be all those images - nearly 1Mb on the homepage.
If you want a faster site: send less data and use decent hosting.
Test your site speed. Before you do anything else, you should test how fast your mobile site really is.
You might think it loads just fine, but it could be slower than you think. One of the best mobile tests is from Think With Google: Enter your URL into the search bar and click “Test Now.” You’ll want to enter your regular URL and not your mobile URL if you have one (e.g., m.site.com).