One of the most common errors, when people want to learn a new skill such as speaking a language, is to focus too much on theoretical knowledge rather than on methods to acquire the skill. That is often why people tend to not clearly differentiate between these two aspects of learning.
For example, think about a person who can craft very fine ceramic pottery and a person who knows a lot about the different techniques of pottery but has never done one himself. These two persons have very different abilities. One has skills that are embedded in how he moves the hands while doing the pottery, the pressures, and the movement that he applies to the material and the internal feeling that he acquired for these gestures. The other person knows a lot about pottery making and can probably distinguish valuable pottery for a cheap one but he would not be able to produce a valuable one himself.
Applying the minimum dose concept to language learning
I think that a good approach is to learn a minimum dose of related theoretical knowledge (grammar in this case) and then practice the target skill (speak in this case, or other exercises). The minimum dose in medicine refers to “the smallest dose of a medicine or drug that will produce an effect”. Similarly, when we learn a language the minimum dose of grammar is the quantity of knowledge that we need to gradually and incrementally improve and practice our ability to read, speak, and understand.
Once we achieve the ability to transfer that initial piece of theoretical knowledge into a skill we can add a new piece of theoretical knowledge and then practice it as a skill again. That is why learning by doing is such a powerful way to learn skills. Because you are forced to practice the skill from the beginning before you acquire too much theoretical knowledge.
Language schools are often very ineffective because they focus much more on theoretical knowledge rather than skills assuming somehow that once one has theoretical knowledge about a subject the skill will follow naturally.