  We present real space quantum Monte Carlo (QMC) calculations of the scandate
LaScO$_3$ that proved to be challenging for traditional electronic structure
approaches due to strong correlation effects resulting in inaccurate band gaps
from DFT and $GW$ methods when compared with existing experimental data.
Besides calculating an accurate QMC band gap corrected for supercell size
biases and in agreement with numerous experiments, we also predict the cohesive
energy of the crystal using the standard fixed-node QMC without any empirical
or non-variational parameters. We show that promotion (optical) gap and
fundamental gap agree with each other illustrating a clear absence of
significant excitonic effects in the ideal crystal. We obtained these results
in perfect consistency in two independent tracks that employ different basis
sets (plane wave vs. localized gaussians), different codes for generating
orbitals (\textsc{Quantum Espresso} vs. \textsc{Crystal}), different QMC codes
(\textsc{Qmcpack} vs. \textsc{Qwalk}) and different high-accuracy
pseudopotentials (ccECPs vs. Troullier-Martins) presenting the maturity and
consistency of QMC methodology and tools for studies of strongly correlated
problems.
