Although it could be a problem if too many parents withdrew their children from school：

因为although 从句是一个“含有虚拟条件句的复合句”，把although 去掉分析这个虚拟语气句：

It could be a problem if too many parents withdrew their children from school.

这个句子一眼就可看出，是一个与现在情况不符或相反的虚拟语气句：

主句是could，从句是withdrew。

句意是：如果有太多的父母使他们的孩子从学校退学，这会是个大的社会问题。

这个句子表示虚拟意义，应该很好理解。因为现在的父母都希望自己的孩子接受教育（极个别的父母除外，父母使他们的孩子从学校退学的情况非常少）。所以，作者就做了这个假设：“如果太多的父母...，那将会是一个...”

下面，我们让这个主从句，做一次“让步从句”，就还原到原来的句子；或者变成并列分句：

1. Although it could be a problem if too many parents withdrew their children from school, it is a suitable option. 

2. It could be a problem if too many parents withdrew their children from school, but it is a suitable option.