B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 8012
Situational Awareness
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Environment - Non Weather Related
We had a 757-300 in front of us on the JFUND 2 arrival into BOS. We were in and out of his wake due to the tailwind on the arrival; so as PF I suggested we ask for a 1 mile right offset. PM agreed; ATC granted. We were 'descend via' on the arrival. I put the offset into the FMC and it began the offset; then said unable after some fix (can't remember for sure...I think it was JFUND). Abeam that fix; it went to CWS (Control Wheel Steering) Right; but stayed in VNAV PTH; so I said I would just use CWS Right to stay Right 1.0 manually (VNAV PTH was still engaged). Prior to SPYSD; we received an approach change from ATC. PM changed it in the FMC (same runway; same transition; ILS 33L now vs Light Visual 33L) and I agreed and PM executed. The path disappeared (not uncommon while it recalculates momentarily) but this happened just prior to SPYSD and we descended below 7;000 prior to SPYSD before the Path came back up. About the time I realized we were low (about 200) ATC gave us a 'descend and maintain 3;000' clearance. I don't think there was any conflict with anyone else; but it bruised my ego.
[Report narrative contained no additional information.]
B737NG flight crew reported an altitude deviation on arrival into BOS.