My family is from Serbia (my parents were both mathematics teachers in Serbia) and I was raised here in Australia. It's definitely true that the curriculum is many years behind even relatively poor and corrupt countries (like Serbia). As a toy example, my parents taught me how to solve simultaneous equations in year 4 (when they'd have taught it in Serbia) while everyone else had to wait until year 9 to learn it in school.

I had friends who came to Australia after starting their education in Singapore, and they were continually shocked how far behind we were. It's honestly gob-smacking how little is being done about this, we're doing a massive disservice to our young people which they will have to overcome for the rest of their lives.