Latest data from the rail company, covering 30 April to 27 May this year, shows less than 50 per cent of services were on time at 22 stations.
Scottish Labour has called on transport minister Humza Yousaf to demand ScotRail makes improvements over the summer to prevent a re-run of last autumn and winter’s travel chaos.
Of the 73 stations in the ScotRail performance report, 22 stations had an on-time performance of under 50 per cent.
The top three under-performing routes were Ardrossan Harbour, with less than a quarter of trains arriving on time (24.5 per cent); Milngavie with slightly more than a quarter arriving as timetabled (25.6 per cent) and Largs with just over a third (33.1 per cent).
However, the ScotRail Alliance said 98 per cent of its services arrived on time last week.
The public performance measure (PPM) is the percentage of booked services arriving within five minutes of their booked arrival time, having called at all booked stations on the route.
“On-time” is defined as the percentage of booked services arriving within 59 seconds of booked arrival time, having called at all booked stations on the route.
The rail operator’s report lists six incidents in May, including signal and points failures, which caused significant delays and cancellations to services.
Neil Bibby MSP, Scottish Labour transport spokesman, described the figures as “unacceptable”.
He said: “These latest results may have a positive headline figure, but the devil is always in the detail.
“The fact fewer than half of services arrive on time at 22 stations is quite frankly unacceptable. Public satisfaction with ScotRail is at a 14-year low and passengers are losing patience with transport minister Humza Yousaf’s failure to act.
“They are fed up with overcrowded, delayed and cancelled trains.
“Mr Yousaf cannot allow a repeat of the chaos that blighted the rail network last autumn and winter, and that means getting on top of performance when weather is better during the summer months.”
A Transport Scotland spokeswoman said: “Only yesterday the ScotRail Alliance announced its best ever performance since taking over the franchise, with 95 per cent of trains running on time last week.
“However, there is no room for complacency.
“The ScotRail franchise contains the toughest quality regime in the UK to drive up standards.
“We have also secured a straightforward Delay Repay process whereby passengers on ScotRail can claim compensation if their service is delayed over 30 minutes.
“The figures quoted are not the industry-wide recognised measurement for train performance.
“The benchmarks in the franchise are expressed in terms of the PPM measure, which is the industry standard in Great Britain, and compared to the rest of the UK, ScotRail performance compares very favourably.”
There are 73 stations listed in the ScotRail performance report. Of those, 22 recorded an on-time performance of less than 50 per cent.
“On-time” means booked services which arrive within 59 seconds of their booked arrival time, having called at all booked stations on the route.
Ardrossan Harbour: 24.50%
Paisley Canal: 40.80%