New figures show that 93.2 per cent of services arrived within five minutes of schedule in the period from February 5 to March 4.
The total is 1.6 percentage points up on the previous four weeks and 1.6 percentage points better than the same period last year.
The annual average performance figure has risen to 90.3 per cent.
Falling below this benchmark triggered the original performance improvement plan in September 2016.
ScotRail said that while the contractual requirement for the plan has ended, it will “continue to focus on delivering all measures of the plan as part of its everyday operations”.
ScotRail Alliance operations director Perry Ramsey added: “We will continue to focus on delivering the best service to our customers, seeking to make improvements every single day.
“This is what our customers want and is our number one priority.”
ScotRail came under increased scrutiny last year following a series of problems with delayed and cancelled services.
Transport minister Humza Yousaf had previously apologised to passengers and suggested train services could be taken into the public sector in future.
He said: “These latest figures demonstrate clear evidence the performance improvement plan is working and its contribution to lifting performance over the last few months should be acknowledged, particularly as ScotRail has now reached the 90.3 per cent target which contractually lifts them out of improvement plan territory.
“It is equally important to recognise the real efforts made by ScotRail staff who are working hard round the clock, in all weathers, to lift performance and deliver rail services which passengers both desire and deserve.”
Robert Samson, of watchdog Transport Focus, said: “Passengers will be pleased to see the performance improvement plan working and performance gradually improving.
“The results so far are encouraging, with the ScotRail Alliance delivering improved punctuality.
“Improvement period by period must continue to reach the performance levels passengers want and expect. “