“Effective” is an adjective describing everything that has a desired or specific result. It is usually accompanied by a large number of abstract nouns as well as nouns referring to people and activities. For example:

Learning online is an extremely effective solution for those students who do not have the opportunity to attend English classes in their nearest neighbourhood.

Anna is one of the most effective teachers our school has ever had.

“Effective” is also used as a synonym to “operational”. We can use it to speak about laws that become binding in a given period:

The new law will become effective in the next few days.

“Effectual” is used with reference to things rather than people:

The most effectual English course formula remains a mystery to many teachers but not ours.

“Efficacious” comes in handy when we talk about remedies or therapies:

This treatment is efficacious in stopping a cough. 

We use “efficient” when we want to highlight that producing desired results can be achieved with minimum wasted effort or resources. If we use “efficient” for describing people we mean that they are competent or capable of achieving something.

While an efficient teacher runs smooth lessons in a timely and well-organised manner, an effective one does all this, and gets results too.

Many language schools fail to develop basic efficient learning skills in their classrooms.