  We study the star formation rate (SFR) versus molecular gas mass
($M_\mathrm{mol}$) scaling relation from hundreds to thousands parsec scales in
two strongly lensed galaxies at redshift $z\sim 1$, the Cosmic Snake and A521.
We trace SFR using extinction-corrected rest-frame UV observations with the
Hubble Space Telescope (HST), and $M_\mathrm{mol}$ using detections of the
CO(4--3) line with the Atacama Large Millimetre/submillimetre Array (ALMA). The
similar angular resolutions of our HST and ALMA observations of $0.15-0.2\,''$
combined with magnifications reaching $\mu>20$ enable us to resolve structures
in the galaxies of sizes lower than $100\,\mathrm{pc}$. These resolutions are
close to those of nearby galaxies studies. This allows us to investigate for
the first time the Kennicutt-Schmidt (KS) law (SFR-$M_\mathrm{mol}$ surface
densities) at different spatial scales, from galactic scales to $\sim
100\,\mathrm{pc}$ scales, in galaxies at $z\sim 1$. At integrated scales we
find that both galaxies satisfy the KS law defined by galaxies at redshifts
between 1 and 2.5. We test the resolved KS (rKS) law in cells of sizes down to
$200\,\mathrm{pc}$ in the two galaxies. We observe that this relationship
generally holds in these $z\sim 1$ galaxies although its scatter increases
significantly with decreasing spatial scales. We check the scale dependence of
the spatial correlation between the surface densities of SFR and
$M_\mathrm{mol}$ by focussing on apertures centred on individual star-forming
regions and molecular clouds. We conclude that star-forming regions and
molecular clouds become spatially de-correlated at $\lesssim 1\,\mathrm{kpc}$
in the Cosmic Snake, whereas they appear de-correlated at all spatial scales
(from $400\,\mathrm{pc}$ to $6\,\mathrm{kpc}$) in A521.
