See *[scalability][1]* (Wiki)  
>scalability is the ability of a system, network, or process to handle a growing amount of work in a capable manner or its ability to be enlarged to accommodate that growth.  

In the given cases,  
>tools that could help make teachers better, at scale  

implies those that could measure up to the size of the task.  
>people who can do great things at scale.  

similarly implies people who can do great things when those things manifest in a real-life (larger) systems. It is easier to demonstrate a prototype supersonic aircraft, but extremely complex to build a really usable/ commercial product of the same design concept.  

We do not say *on a large scale* in this context, but instead we say *at scale*, because the magnitude could either increase or decrease from time to time. Adapting accordingly and producing comparable results in all cases is a challenge in itself. Think prosthetic & orthotic devices, for one.

 


  [1]: http://en.wikipedia.org/wiki/Scalability