  We present adaptive optics-assisted integral field spectroscopy around the Ha
or Hb lines of 12 gravitationally lensed galaxies obtained with VLT/SINFONI,
Keck/OSIRIS and Gemini/NIFS. We combine these data with previous observations
and investigate the dynamics and star formation properties of 17 lensed
galaxies at z = 1-4. Thanks to gravitational magnification of 1.4 - 90x by
foreground clusters, effective spatial resolutions of 40 - 700 pc are achieved.
The magnification also allows us to probe lower star formation rates and
stellar masses than unlensed samples; our target galaxies feature
dust-corrected SFRs derived from Ha or Hb emission of 0.8 - 40Msol/yr, and
stellar masses M* ~ 4e8 - 6e10 Msol. All of the galaxies have velocity
gradients, with 59% consistent with being rotating discs and a likely merger
fraction of 29%, with the remaining 12% classed as 'undetermined.' We extract
50 star-forming clumps with sizes in the range 60pc - 1kpc from the Ha (or Hb)
maps, and find that their surface brightnesses and their characteristic
luminosities evolve to higher luminosities with redshift. We show that this
evolution can be described by fragmentation on larger scales in gas-rich discs,
and is likely to be driven by evolving gas fractions.
