There hasn't been any change to how sub summary and leading grand summary layout parts function in a very long time--other than FileMaker 10 making them visible in browse mode.
A leading grand summary is not used for grouping data, for that, you need a sub summary layout part. But the records in your found set must be sorted in an order that includes the "when sorted by" field specified for the sub summary layout part or it will not be visible when in Browse mode.
Sub Summary layout parts are also not visible when you use a web browser to access a web published database.
Thank you Phil,
I fixed how you said that, now works perfect.