Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Situational Awareness
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Procedure; Environment - Non Weather Related; Human Factors
Descending on the ZZZZZ 3 Arrival; in FMC level automation both laterally and vertically; we received a clearance to descend and maintain 5;000 feet.  The PF set 5;000 feet in the altitude selector window; and the PM confirmed it.  However; the PF did not press Altitude Intervention; and the PM did not verify that it had been selected.  Therefore; the 9;000 feet crossing restriction at ZZZZZ1 remained in the FMC; and the aircraft leveled at 9;000 feet.  ATC trapped the error; and we continued our descent to 5;000 feet and landed at ZZZ uneventfully.The PM had not flown in almost three weeks and was admittedly a little 'rusty.'  Flying regularly maintains proficiency with skill sets.  This was the first leg of the trip and the PM and PF had never flown together before.  The PF displayed very good attention to detail which may have contributed to the PM's lack of alertness and not challenging the PF when Altitude Intervention was not utilized to erase the 9;000 feet crossing restriction at ZZZZZ1.  The PM must continually be asking his or herself 'What actions would I take to ensure the aircraft does what I want it to do?' even when the PF is demonstrating a high level of proficiency.  Another technique that would have ensured the aircraft's descent all the way to 5;000 feet would have been to utilize MCP level automation such as Level Change or Vertical Speed.
Air carrier First Officer reported not making the second crossing restriction on arrival.