I think it depends on what your hopes and goals are for your child/ren. We sent our boy to local kindy (3 years) through the 8th grade. Then we sent him to Bethany in Gong Guan for an American curriculum where English was the language of instruction, and we had him repeat the 8th grade and then do the 9th grade, there. Our hope and goal was to allow him to be fluently native in both Chinese and English. I think we were successful in our goal. However, it wasn’t as easy as simply sending him to the schools that we did.
Possibly, but, not likely. Are both parents native English speakers? My wife is local, and as a rule never spoke English with the boy. This was helpful in that 1) she could assist with homework while he was in grade school and 2) it helped to support his Chinese language learning at an early age. I always spoke English to the boy, and often took him out with me to places where other native English speakers would be, so that he heard English spoken in accents other than my own. However, the biggest influence in keeping his English up was sending him back to my parents’ house for the summers, where he spoke English daily and interacted daily with only English speakers.
Again, while this is true, whether it is important to you and your child/ren will depend on your goals. Our primary goal in sending our boy to local schools was to attain native proficiency in Chinese. We encouraged him to do his best in his classes, but, never pressured him to compete with his classmates. He did OK. Never burned up the class with his grades. He read lots of stuff outside his school work and learned lots on his own about world history, geography, and even science and nature. But, this type of personal exploration will be difficult unless you support the same and are not too concerned about grade competition in the local schools. We were able to manage this way because we knew that we would be taking the boy out of the local schools and putting him in an international/American school for a couple years to get him ready to go to the US for high school and college (uni).
We never sent our boy to a cram school. Again, this was due to our primary goal of attaining language proficiency.
As indicated above, our boy went to local schools from kindy through the 8th grade. We then sent him to Bethany to start getting used to English as the language of instruction and an American curriculum. It was expensive, but, only half the price of Taipei American School. Was it worth it? Absolutely! The folks at Bethany frequently told us that they had a good school, but, we had no independent verification of this. However, our boy did well there, he loved it there, and he still hangs out with his friends from there when he returns for summers in Taiwan. After only 2 years at Bethany, we sent him to live with my parents and to attend the same public high school that I went to. He did very well there even with difficult classes such as advanced placement economics and government classes. He’s now in college and tearing it up, there.
As stated above, our first goal was always language proficiency. As our boy is a US citizen only (no ROC citizenship), our second goal was getting him into and doing well in the US system. I think we have succeeded in both goals. He just started his junior (3rd year) at college (uni) and is doing very, very well. My wife (a long time Chinese language teacher) says that his Chinese proficiency is native. He did an internship this past summer at the Pennsylvania Office of Trade and Investment in Taipei, and he was the only student intern who was fluent in both Chinese and English. The students from the US had virtually no Chinese proficiency and the Taiwanese uni students had low levels of English proficiency. As a result, the boy was very busy and I think he had a solid internship experience.
So, before you even ask the questions that you (the general you, not you personally) have posed above, it makes good sense to first understand your own long-term goals for your child/ren.