Welshpool Church in Wales Primary School was opened by Powys County Council in January 2021 as part of its Transforming Education programme.
The project experienced a number of setbacks since the original business case was approved in 2017, including the Cadw listing of Ysgol Maesydre, the collapse of the main contractors with the school partially built, the impact of Covid-19, and inflationary costs.
Since the school opened, external access and highways works have been carried out and they were completed last summer.
Powys County Council said the £150,000 overspend for the project is related to the external works.
Cabinet will consider the matter on Tuesday, May 23, where they will be asked to approve additional funding of £150,000 for the project now the accounts have been finalised.
The cabinet will also be asked to set up a review of the costs of the project.
Councillor Pete Roberts, cabinet member for a Learning Powys, said: "Welshpool Church in Wales Primary School is a fantastic facility that has significantly improved the learning environment for local pupils.
"However, the collapse of our construction partner forced the previous cabinet into a change of direction with cost increases at several points in its development. This paper identifies the last of those expenses in a final report.
"There is much to be learnt from the management of this project and I will be recommending to cabinet that the full review of costs and lessons learnt that I previously called for as a scrutiny chair will now be undertaken.
"This will include both Welshpool school projects with the findings being shared with the Governance and Audit Committee's Capital Working Group."