We are trying to achieve CMMI Maturity Level (ML) 3 in my company and we have decided to skip ML 2. So, now, one of our problems is related to software size estimation. We defined a proprietary method, based on Use Case Points and Function Points, but the practitioners are struggling with it. From your experience, what other methods have you seen or implemented in the companies with this same problem? Or, if a proprietary method was defined, what were the main aspects to take in account?
I would strongly urge you to forget the ML 3 Process Areas until you have mastered ML 2. There is a fundamental difference between how a ML 2 Project Manager approaches Project Planning (PP) and Project Monitoring and Control (PMC) vs. a ML 3 Project Manager. Estimation being one of the differences. Use Case Points and Functions Points are fairly sophisticated concepts and there are challenges with getting consistency in determining what each of these things are. I would recommend that you take a step back from the model and the projects and look at your historical project data. Use the actual effort, costs, etc. from previous projects to estimate a new project. Forget about Use Case Points and Function Points for now. Once you have mastered being able to use historical information to build an empirical estimation model, then it might make sense to add a layer of sophistication by considering Use Case Points or Function Points.
Another recommendation is let the Project Manager create the project estimates and then review them with the practitioners as a sanity check rather than ask the practitioners to create the estimates. Over time as the organization gains experience estimating projects etc., then it makes sense to involve the practitioners up front in the estimation process. You have to learn to crawl first with estimation before you can sprint with the big boys.