Here is something interesting since you mentioned 3 landings in 90 days. Student and instructor neither have made 3 takeoff a and landings in 90 days to a full stop for night currency. Can they go fly together to establish currency? Here's an excerpt from an article by Kathy Yodice from AOPA.
"Basically, this is my question: If I had a flight instructor on board the aircraft during my night flight to gain night currency, and if the flight instructor--like me--was not night current, would the flight be in violation of the regulation? At first, I would think to say "Yes, that's a violation because neither one of the pilots is night current to be able to carry another person on board the aircraft." But, the FAA says, "No, it would not be a violation because neither pilot is a passenger." Here's what the FAA says:
We agree that, for purposes of section 61.57(b), an authorized instructor providing instruction in an aircraft is not considered a passenger with respect to the person receiving instruction, even where the person receiving the instruction is acting as PIC. (The instructor must be current, qualified to instruct, and hold a category, class, and type rating in the aircraft, if a class and type rating is required.) The instructor is not a passenger because he is present specifically to train the person receiving instruction. Neither is the person receiving instruction a passenger with respect to the instructor. This training may take place, even though neither pilot has met the 61.57(b) requirements.
So, not only is it legal to take a night flight when you and your flight instructor are not night current, but both may also log it as PIC. But be careful--only a pilot who is the sole manipulator of the controls for three full-stop landings at night would be able to log the landings for purposes of night currency under FAR 61.57(b). That's something to consider when you need to get night current."
She specifically addresses night currency here. I wonder if the the same would apply for day instruction. Seems it would based on the FAA's explanation.
