I would say yes, definitely. If the second language is not mastered very well, grammar should be taught explicitly, whereas if the L2 speakers are proficient, then the teaching should perhaps be implicit (e.g., by exposing students to film dialogues and by asking them to "guess" the grammar rules behind their conversations etc.).
Well, any grammar is abstract by nature. Teaching grammar requires a certain level of students' abstract thinking. So if you start explaining Present Perfect Passive to an 8 year old child, you are not likely to seriously expect considerable progress. But studying grammar at the age of 15 is time well spent.
At tender age, cliches, phrases, syntactic structures should be repeatedly, even monotonously introduced without too much theory. Fairy tales point in the right direction: core vocabulary + simple structures. IMHO
I think that by combining explicit grammar instruction with opportunities for authentic communication and language exploration, educators can help students develop the linguistic skills and confidence required to succeed in a variety of academic and professional settings.