I teach adults almost exclusively. I teach one-on-one about 90% and small group classes about 10%. My students are typically professionals with university degrees.
As I said earlier, most of my Spanish speaking students are prepared to be in 100% English course. But some get so frustrated they just start speaking to me in Spanish to express how hard they find the language learning process. In the past, I would stop them and explain that I didnāt understand Spanish. But now, if they speak slowly, I get the gist. And then I answer them in English 
Or sometimes they say āComo se dice⦠en Ingles?ā Nowadays, I sometimes have the answer.
Nowadays, I think my classes are 98% English, 2% Spanish.
Hereās the example I want to make about efficiency and how Iāve begun to break with the monolingual orthodoxy.
FIrst about 80% of class focus is conversation, reading, and listening to material my students find personally relevant and/or professionally interesting. About 20% of my focus is on helping my student with specific grammar or vocabulary lessons where they have a clear need.
with my A2 to b2 students, I have observed several high frequency, near-universal mistakes when speaking. Almost all of my students make a lot errors with verb + gerund or verb +infinitive structures like:
āI enjoy to swimā āHe keep to talk.ā āWe need using Uberā āDo you want dancing with meā āI needed to went to my hotelā etc.
I keep a notebook of corrections for my students. After making the corrections in the notebook for a few days, I ask them to focus on a couple of units in Cambridgeās āGrammar in Useā. I teach verb + infinitive one day, and verb + gerund the other day. Many students find the examples and exercises totally confusing and unhelpful.
For years I believed that the structures must be wildly different in Spanish, and thus this must the reason for these nearly universal speaking mistakes, and seemingly increased confusion after teaching the units.
But after a learning Spanish on LingQ for the last 12 months, I recently realized, āHold on! These structures are grammatically similar to English!ā So in the last three months, after doing half of each verb + gerund / Verb + infinitive unit together in class, I ask my students to translate a few example sentences into Spanish:
āShe enjoys dancingā
āDo you want to dance?ā
āShe keeps workingā
āThey need to workā
And then I ask my students to explain the structures of the Spanish. And then compare the structures to English. This seems to be the moment when a light bulb goes off, instead of continued frustration.
I also have been asking a few of my students to translate some examples of the present perfect in Spanish into English (and vice versa) to show them how remarkably similar that tense is in both languages-- but only after my student complains about not understanding English verb tenses like the present perfect!
This is the āunorthodoxā bilingual shortcut Iām talking about.