Writeshop until 5tu grade then IEW?

[My4arrows]

We have been using writeshop for a gentle intro to writing. My odd will be in 4th next year and I had considered using IEW. Bit seeing writeshop d in the build your bundle I'm stated thinking of keeping writeshop and then beginning IEW in 6th grade. Will changing curriculum at that time be too difficult for the kids( especially if they aren't strong writers already?)