说的简明一些就是：

在表示“确保” 意义的词语后面，其宾语从句使用一般时态取代将来时态。

从逻辑分析，究其原因：“确保” 二字，表示不能含糊，保证务必做到。所以不存在“可能性”，因为will 和would 表将来，带有“不确定性”，而且隐含着“推测和可能”。所以，我们用一般现在时取代一般将来时；用一般过去时取代过去将来时。

“确保”的英文一族：

make sure that；

be sure that；

ensure that；

insure that；

assure that；

使用一般时态的例句很多，网友可以自己查一下。

【说明】随着英语的发展，用将来时的情况其实也很多。网友的句子改为would take part 也不算错。例如：

I can't ensure that he will be there on time.
我不能保证他会及时到那儿。

They ensured that he would obtain the prize. 

他们保证他会获奖。

By making these programmes optional, schools would ensure that only motivated students took part.

(1) 

中学所学的是make sure后用现在时表示将来:

Make sure (that) they do not escape.

I will make sure that the letter leaves tonight.

(2)

Learning about first aid is the best way to make sure that we will not feel that we could have done more. (Correct)

问：为何这里用了将来时？

答：make sure 后可以用 现在时，过去时，将来时。

##  make sure + will do / do的选择问题

make sure 几个基本的含义：

1. be careful to do ；don't forget to do; （务必、别忘了----> 确保） 

2. verify (核实；证实-----> 弄明白)

当表示1. 的意思时，常用现在时，这种情况，含有命令口吻时，后面也接一般时，其实是某种形式的虚拟语气；而表示2. 的意思时，如果时间上有将来的含义（或者说描述一种事实），则用将来时。

(3)

1. You've just got to make sure you tell him （Correct）/ will tell him. (Wrong)

答： 本句make sure的意思是be careful to do ；don't forget to do；

另外，这里用will tell 还有will本身情态动词带来的含义：“执意要”(如果重音读在will上)，“想要”这当然是没有意义的

2. Learning about first aid is the best way to make sure that we will not feel that we could have done more. (Correct)

答：这句是verify的含义，搞清楚，指将来。

它 = Learning about first aid is the best way to make sure that we render aid and after that we will not feel that we could have done more

(4) 回到题目：

By making these programmes optional, schools would ensure that only motivated students took part.

这里是“确保”的意思，用现在时，但句子时间框架是过去的，故自然跟着用过去式