They were identified as a family by John Z'graggen in 1971 and linked with the Sepik languages by Donald Laycock two years later.
Malcolm Ross (2005) classifies them as one branch of a Ramu – Lower Sepik language family.
The first five, sometimes classified together as Lower Ramu, are relatable through lexical data, so their relationship is widely accepted.
Laycock (1973) also includes the Piawi languages as a branch, but Ross (2005), Foley (2005) and Usher all reject their inclusion.
The pronouns reconstructed by Ross (2005) for Proto-Ramu are: However, Grass languages have the innovations *ɲi ‘1SG’ and *re ‘3SG’.