First and foremost, examine your reasons for wanting your children to learn Mandarin. For me, it is because I am ethnically Chinese and grew up learning and speaking Mandarin. It is important to me that my children not only know the language but they understand and appreciate the culture. Not so much because they need to be able to communicate with my parents, but because this is a part of their heritage.
You can find numerous research touting the benefits of bilingualism, such as academic achievement, cultural awareness, brain health, job opportunities, etc. The advantages of learning and speaking a second language outnumber the disadvantages.
However, not all Mandarin immersion schools are created equally. How long has the program been around? What Mandarin curriculum is the school using? My daughter's K-8 school starts with 80/20 exposure in the K/1 years (i.e. 80% in Chinese) and by the time the students get to 8th grade, it is 30/70 with 30% of instruction in Chinese.
Some questions to ask yourself include:
1) Is the school able to hire certified teachers and provide teachers with the necessary support and teacher training? Classroom and behavior management skills are equally important. Some teachers are hired straight out of Asia with no understanding of how to teach in an American school or an International School. There is a misalignment of expectations between the teachers and parents from classroom conduct to the amount of Chinese homework assigned.
2) What is the retention rate for Chinese teachers at the immersion school? Do teachers often leave after a year or two of teaching? Are the teachers "trainee" teachers that leave after a few months of teaching?
3) Is the school able to provide resources and support to students who need it? My daughter's K-8 Mandarin immersion school had a Homework Club to help students with their Chinese homework after school. The school also organized Chinese camps in the summer and trips to China for different grade levels. Does the school encourage parent involvement and do parents get involved? Are there cultural activities organized by the school or parents? Schools and families can work closely together to foster a close-knit community that can be extremely enriching culturally for students.
Are there supplementary Mandarin learning resources for students outside of school? Heart Strings Mandarin's fun, music-based approach to learning Mandarin takes the drudgery out of learning Mandarin. Several Mandarin immersion schools have listed Heart Strings Mandarin's online classes as an additional resource for families.
When families feel unsupported and their children are overwhelmed and struggling with learning Mandarin, that's when they drop out of the Mandarin immersion program after a few years.
